The present invention relates to a retractor (a winding device) for use in a seat belt device, particularly, to an improved retractor with a clamp mechanism which holds a webbing directly between two parts thereof in a vehicle emergency to minimize the amount of drawing-out of the webbing.
Conventionally, there has been employed a seat belt device which restrains an occupant or the like in a vehicle to protect the occupant against collision shocks. The seat belt device employs a retractor of a type including not only an emergency lock mechanism which, in a vehicle emergency such as a collision or the like, locks the rotation of a winding shaft with a webbing wound thereround in the webbing draw-out direction but also a clamp mechanism which holds the webbing between two parts thereof to prevent the extension of a seat belt, thereby improving the occupant restraining performance thereof in the early stage of the vehicle collision.
However, there is a possibility that a force greater than the break strength of the webbing can be applied to the webbing held by the clamp mechanism in the vehicle emergency such as a collision or the like. That is, if a strong tensile force to draw out the webbing is further applied to the retractor which prevents the extension of the seat belt by the clamp mechanism, then a force to hold the webbing more strongly is collectively applied to the webbing holding portion, so that there is the possibility that the webbing would be broken in the webbing holding portion. Also, if the shock due to the collision is very great, then a sudden deceleration is applied to the body of the occupant, with the result that a load to be applied to the occupant by the seat belt can be increased.
In order to avoid the above problems, for example, a retractor with a clamp disclosed in U.S. Pat. No. 5,154,368, U.S. Pat. No. 5,299,854, Unexamined Japanese Utility Model Publication No. 4-43550 and various other retractors including a clamp mechanism which, if a tensile force of a predetermined force or greater is applied to the webbing, a part of a rotary holding member holding the webbing is deformed a part of a case (a retractor base) or a shaft supporting one end portion of the rotary holding member rotatably is broken to remove the force that holds the webbing have been proposed. That is, in such clamp mechanism, by removing the operation of the clamp mechanism to allow the seat belt to be played out a predetermined amount, a deceleration generated in the body of the occupant is relieved to protect the occupant's body more surely as well as to prevent damage of the webbing.
On the other hand, as a clamp mechanism, unlike the above-mentioned clamp mechanism in which the rotary hold member with one end portion thereof rotatably supported by the retractor base holds the webbing to prevent the extension of the seat belt, there is proposed another clamp mechanism in which a wedge-shaped clamp member is inserted between the sliding contact surface of a guide member fixed to a retractor base and a base back plate to hold a webbing to prevent the extension of a seat belt. However, in the last-mentioned type of clamp mechanism, various clamp removing mechanisms which can be provided in the former type of clamp mechanisms cannot be applied because the parts of the last-mentioned type of clamp mechanism are different from those employed in the former type of clamp mechanisms.
In view of the above circumstances, as a clamp removal mechanism that can be applied to the clamp mechanism using a wedge-shaped clamp member, a clamp removal mechanism is disclosed in U.S. Pat. No. 5,242,213, Unexamined Japanese Utility Model Publication No. 4-43551, and the like.
In the clamp removal mechanism disclosed in U.S. Pat. No. 5,242,213, a belt retracting device (a retractor) and a webbing clamping device (a clamp mechanism) are connected by a connecting device which, simultaneously when reaching a stipulated value of stress, deforms elastically to move apart from the belt retracting device to allow the limited motion of the webbing clamping device. And, if a webbing pulling force of a stipulated load value or more is applied to the webbing clamping device, then the connecting device is broken to thereby release the holding of the webbing by the webbing clamping device.
Also, in the clamp removing mechanism disclosed in Unexamined Japanese Utility Model Publication No. 4-43551, a holding portion (a teeth portion) to be provided on the surface of a holding device opposed to a webbing is arranged such that it can be sheared with a pulling force to be applied to the webbing, and thus, if a pulling force of a predetermined value or greater is applied to the webbing, then the holding portion can be sheared to release the holding of the webbing by the holding device.
However, in a retractor incorporating the clamp removing mechanism disclosed in U.S. Pat. No. 5,242,213, if a webbing pulling force of a predetermined value or greater is given to the webbing clamping device, then the connecting device is broken and the webbing clamping device moves apart from the belt retracting device and a vehicle body space for storing the retractor is inevitably enlarged to allow the movement of the belt retractor, which results in poor vehicle mounting efficiency.
Also, in a retractor incorporating the clamp removing mechanism disclosed in Unexamined Japanese Utility Model Publication No. 4-43551, if a webbing pulling force of a predetermined value or greater is applied to the holding device, then the holding device is sheared to thereby remove the webbing holding force with the result that the webbing tension acting on the webbing is caused to decrease suddenly. At the same time, if the rotation of a winding shaft in the webbing drawing-out direction is locked by an emergency lock mechanism, then the webbing tension is caused to rise suddenly again. Therefore, the webbing tension often increases or decreases to thereby vary greatly the deceleration that acts on the body of the occupant. Also, since the webbing tension falls greatly from the time when the webbing holding force is removed to the time when the webbing holding force rises again, it is difficult to absorb efficiently the kinetic energy that is produced by the occupant's body in a collision.